Analytical system and method for measuring and controlling a production process

ABSTRACT

An analytical system for analysing and controlling a shaping process for glass products is described. The analytical system comprises an infrared-sensitive measurement system and a processor communicating therewith, the infrared-sensitive measurement system being equipped to measure infrared radiation originating from hot glass products immediately after the shaping process for the glass products and the processor being equipped to determine a heat distribution in the glass products on the basis of information determined by the measurement system. Because the infrared-sensitive measurement system is sensitive only to radiation in the so-called Near Infra Red (NIR) region, radiation originating from the interior of the glass wall can be measured. This makes novel analytical methods possible with which, inter alia, a distinction can be made between a change in glass wall thickness and a change in temperature.

The present invention relates to an analytical system for analysing andcontrolling a production process for glass products, the productionprocess comprising a shaping process and a cooling process and theanalytical system comprising an infrared-sensitive measurement systemand a processor communicating therewith, the infrared-sensitivemeasurement system being equipped to measure infrared radiationoriginating from hot glass products immediately after a shaping processfor the glass products and the processor being equipped to determine aheat distribution in the glass products on the basis of informationdetermined by the measurement system.

A system of this type is disclosed in the patent EP 643 297 A1. Thispatent describes an analytical system that can be used to determine thequality of glass products before the glass products have cooled. Thequality of the products is determined by determining the heatdistribution in a product and comparing this with a reference heatdistribution from a mathematical model. If a specific product does notmeet specific criteria, this product is removed from the productionprocess before it has cooled. In this way it is possible to useadditional information from the glass shaping process, which would belost during a cooling process, to determine the cause of a productionfault. By this means it is possible to adjust the shaping process ingood time, if necessary.

A disadvantage of this infrared measurement system is, however, the verylow sensitivity to changes in temperature, glass purity and glassthickness in the interior of the glass wall. Specifically, glass iscompletely opaque to the major proportion of the infrared spectrum sincethe glass has a high coefficient of absorption for infrared radiation.As a result the infrared radiation from the interior of the glass wallis completely absorbed. Thus, only the infrared radiation originatingfrom a thin surface layer is measured. Consequently, changes in theinterior of the glass wall beneath this surface layer cannot bedetermined. The infrared radiation from the surface layer as it wereblinds the infrared sensors to the small amount of radiation thatoriginates from the interior of the glass wall. Partly because of thisit is impossible to determine whether the change in the infraredradiation is caused by a change in glass wall thickness or by a changein the temperature of the glass wall. Specifically, an increase in theintensity of the infrared radiation signifies a higher temperature ofthe glass surface on the outside of the product. This can be caused by athicker glass wall, as a result of which the product cools less rapidly,or it can be caused because the temperature of the product is higher.Since only the radiation from the glass surface is measured usinginfrared, it is not possible to distinguish between these two causes.

One aim of the present invention is to be able to measure infraredradiation originating from the interior of the glass wall of hot glassproducts.

In order to achieve this aim, the present invention relates to ananalytical system of the type mentioned in the preamble, characterisedin that the infrared-sensitive measurement system is sensitive only toradiation in the so-called Near Infra Red (NIR) region.

Infrared light with long wavelengths is completely absorbed in theinterior of the glass wall. This is not the case with NIR radiation. NIRradiation essentially originates from the interior of the glass wall andthe measured amount of NIR radiation is thus correlated to the amount ofheat in the interior of the glass wall.

Preferably, the infrared-sensitive measurement system is sensitive towavelengths of between 900 and 2800 nanometres. It has been found thatoptimum results are obtained at these wavelengths.

In one embodiment of the invention the measurement system comprises atleast one infrared sensor and at least one Near Infra Red filter.Preferably, the transmission characteristic of the Near Infra Red filteris dependent on the colour and the specific material composition of theglass products. This ensures optimum measurement sensitivity.

In a preferred embodiment the processor is equipped to carry out thefollowing steps:

-   -   (a) subdividing an image of the glass products into at least two        measurement regions;    -   (b) determining average intensity values for the different        measurement regions for consecutive glass products;    -   (c) determining, for at least two measurement regions, a current        average value from the average intensity values determined for a        number of consecutively shaped glass products over time;    -   (d) recording, for each of the at least two measurement regions,        any deviation between the current intensity or the current        average intensity and a reference value;    -   (e) comparing any deviations between the at least two        measurement regions;    -   (f) generating an error signal in the event of any deviations.

By analysing the deviations between the at least two measurement regionsit is possible to determine whether a change in glass wall thickness hasoccurred or whether a change in temperature has occurred. In thiscontext change signifies a change with respect to the previous glassproducts and glass products produced in the past

In another embodiment the processor is equipped to carry out thefollowing steps:

-   -   (a) subdividing an image of the glass products into at least two        measurement regions;    -   (b) determining average intensity values for the different        measurement regions for consecutive glass products;    -   (c) determining a machine plot by plotting a graph of the        average intensity values as a function of the consecutive glass        products, i.e. stations;    -   (d) determining a cooling plot by means of an optimum fit curve;    -   (e) recording any deviations between a current machine plot and        the cooling plot;    -   (f) generating an error signal in the event of any deviations.

By determining an optimum fit curve and taking this as reference curve,current machine plots can be compared with this. This can be performedindividually for each measurement region. Deviations in the machineplots compared with the fit curve provide information on errors in theshaping process. By means of this analytical method both the quality ofthe shaping process and also the quality of the glass products can bemonitored. If the measured intensities are precisely on the coolingplot, the glass products will have the same quality.

In another embodiment the processor is equipped to record localdiscontinuities in the heat distribution in a glass product. With theaid of this analytical system the heat distribution of the heat from theinterior of the glass wall can be determined. If material foreign toglass, glass of a different composition, a lower amount of glass(blister, air bubble) or a higher amount of glass (glass fragment orglass point) is present in the glass wall this will result in a localdiscontinuity in the heat distribution. Such a local discontinuity isthe result of a change in the purity of the glass.

Furthermore, the present invention relates to a method for analysing andcontrolling a shaping process for glass products, as described in claim13. By measuring radiation in the Near Infra Red region the heatdistribution in the interior of the glass wall can be determined, whichoffers possibilities for novel analytical methods.

One embodiment of the abovementioned method is described in claim 18.Although the intensity of the measured radiation is dependent on thetemperature distribution, the amount of glass and the materialproperties, changes in the thickness of the glass wall can readily bedetermined by means of this method. By comparing the deviations fromaverage intensities in two measurement regions it is possible todetermine whether the change in the measured radiation is to be ascribedto a change in the thickness of the glass wall or to a change in thetemperature of the glass. This analytical method will be explained inmore detail in the description of the figures.

Another embodiment of the method according to the invention is describedin claim 21. With the aid of this method the correct settings for theshaping process can rapidly be determined and a setup time in the caseof a change in production is shortened. Moreover, deviations in thecurrent machine plots for the different measurement regions can be usedto analyse faults in individual sub-processes of the shaping process.

Further advantages and characteristics of the present invention willbecome clear on the basis of a description of a number of embodiments,reference being made to the appended drawings, in which:

FIG. 1 shows a production process from the state of the art,

FIG. 2 shows, diagrammatically, a glass shaping machine and ameasurement system from the state of the art,

FIG. 3 shows, diagrammatically, a measurement system according to theinvention,

FIG. 4 shows an example of a subdivision of the glass products intomeasurement regions.

FIG. 5 is a graph showing the change in the average intensity of twomeasurement regions and a reference value,

FIG. 6 is a graph showing the change in the average intensity of twomeasurement regions and a reference value,

FIG. 7 is a graph of a so-called machine plot,

FIG. 8 is a graph of a so-called machine plot with a fit curve.

FIG. 1 shows a known production process for hollow glass products inwhich various process steps can be recognised. In a melting furnace 1recycled glass fragments, mixed with basic raw material and additives,are remelted to give liquid glass. The molten glass flows from themelting furnace 1 via one or more channels 2 (“forehearth”) to a feeder3. Downstream of the feeder 3 the stream of glass is cut into glass gobsin a gob forming process 4. The glass gobs are then fed via a gobtransport 5 to an Independent Section (IS) machine 6.

The IS machine 6 in which the shaping process takes place is shown inmore detail in FIG. 2. In the IS machine 6 each glass gob is shaped intoa product. The shaping process is, for example, carried out with the aidof two moulds. The gob first falls into a first mould (the so-calledblank mould 11) where, depending on the shaping process, the first stageof the product is blown or pressed. This first stage of the product,also termed the parison, is then transported to a second mould (theso-called blow mould 12), where the parison is blown to give the finalshape of a glass product 18. The section 16 with the two moulds is alsotermed a station. The IS machine 6 consists of several parallel sections14. Each section 14 can, in turn, consist of several stations 16 whichare able to produce products independently of one another. The blownglass products 18 are placed one after the other on a conveyor belt 8and fed to a cooling oven 7; see FIG. 1. In the cooling oven 7 theproducts are heated to above the so-called annealing point of the glass.The products are rendered stress-free by this means. The products cannow cool and can be packed and transported to their destination. Thesection of the production process downstream of the cooling oven is alsotermed the “cold” section of the production area During production awide variety of faults which have an adverse effect on the quality ofthe glass product can arise in every process step. Consequently it isnecessary for the process variables of each process step to be setwithin very narrow tolerances and to be monitored. These processsettings are dependent on the type of end product and have to bere-adjusted for the production of a different type of product (theso-called product change). An end product 18 of good quality has thecorrect dimensions, has a uniform glass thickness, does not have anycracks, has an even colour and has a high degree of glass purity. Glasspurity means that the glass must be free from all sorts of materialforeign to glass, such as grit, air bubbles, metals and contamination.

In order to be able to offer the customer glass products 18 of aconsistently high quality, the glass products are inspected to determinetheir quality. To prevent information from the shaping process beinglost by the annealing process, currently use is made of an infraredmeasurement system 20, see FIG. 2, which measures the thermal radiationby the glass product 18 before the glass product enters the cooling oven7. The information obtained by the infrared measurement system 20 can beused to monitor the quality of the glass products 18 and the process.The known measurement system 20 has the disadvantages mentioned above.

FIG. 3 shows, diagrammatically, a novel measurement system 30 accordingto an embodiment of the invention. The measurement system 30 comprises afilter system 34, at least one infrared sensor 32 and a digitalprocessor 38. The filter system 34 allows selective transmission only ofinfrared radiation in the Near Infra Red (NIR) region, that is to sayradiation having a wavelength of between 600 and 5000 nanometres.Thermal radiation in the NIR region mainly originates from the interiorof a glass wall 36. Preferably the filter system is so equipped that itallows the transmission of radiation in the wavelength range of 900 to2800 nanometers, depending on the specific composition of the glass. InFIG. 3 the NIR radiation is shown by the thin dashed arrows. The digitalprocessor 38 is equipped to analyse a heat distribution in a glassproduct on the basis of measurement data. This can take place in variousways, which are described in the embodiments below.

In one embodiment the digital processor 38 is equipped to subdivide theheat distribution obtained for a glass product into so-calledmeasurement regions 40, 41, 42, 43, 44; see FIG. 4. These can be anumber of strips that subdivide the image of the glass product 18 intohorizontal measurement regions 40, 41, 42, 43, 44 (see FIG. 4), but adifferent form of measurement regions 40, 41, 42, 43, 44 is alsopossible. The number of measurement regions 40, 41, 42, 43, 44 is two ormore. The number of measurement regions is not relevant, but moredetailed information on the shaping process is obtained with a largernumber of measurement regions. The measured intensities of the radiationare preferably averaged over each measurement region 40, 41, 42, 43, 44.The current average value thus obtained is compared with a referencevalue. This reference value is determined by the cooling curveoriginating from the measurement region or by another statisticalcalculation such as, for example, the running average. If the currentaverage value is greater than the reference value the difference is‘positive’; see FIG. 5. If the average value is lower than its referencevalue this difference is then ‘negative’.

This analysis is carried out for each measurement region 40, 41, 42, 43,44 set. If there are measurement regions 40, 41, 42, 43, 44 that displaya difference and have an opposite sign the change is to be ascribed to achange in the glass thickness; see FIG. 5. Explanation: each glassproduct is formed from a glass gob. The gobs have a constant weight andvolume. The quantity of glass per product is thus constant. If, as aresult of a disturbance in the process, a thinner glass wall is producedsomewhere in the product, for example in the base section, the glasswall thickness in another measurement region 40, 41, 42, 43, 44 of theproduct then has to increase. The measurement regions 40, 41, 42, 43, 44with a thinner glass wall will emit less radiation; the measurementregions 40, 41, 42, 43, 44 with a thicker glass wall will emit moreradiation. The change cannot be ascribed to a change in the materialproperties since the glass for the products comes from the same furnace.

FIG. 6 shows a graph with a different change in the average intensity ofthe measurement regions 40, 41, 42, 43, 44. As a result of a disturbancein the process a deviation in the radiation occurs. Because in this casethe measured deviation has a matching sign there has been a change inthe glass wall temperature. Explanation: each glass product is formedfrom a glass gob. The gobs have a constant weight and volume. Thequantity of glass per product is thus constant. If, as the result of adisturbance in the process, the temperature of the glass product 18rises, those parts of the glass product 18 that are hotter will then allemit more radiation. Since the thickness of the glass wall has notchanged, the deviations in the relevant measurement regions 40, 41, 42,43, 44 will all have a matching sign for the difference. The changecannot be ascribed to a change in the material properties since theglass for the glass products 18 comes from the same melting furnace 1.

Each section 14 of the IS machine 6 consists of one or more stations 16.Each station 16 can produce a glass product 18 independently of theother sections 14. The glass products 18 that have just been formed arein a fixed sequence on the conveyor belt 8. Depending on the section 14from which they have been produced, the glass products 18 all have adifferent cooling time. This is the time between the end of the shapingprocess and the time when the product passes by the measurement system30.

Because the invention is preferably synchronised over time with the ISmachine 6, the station 16 from which the glass product 18 originates isknown for each glass product 18. In FIG. 7 the measured intensity isplotted against the various stations 16 for one specific measurementregion 40, 41, 42, 43, 44. The names of the stations (B and F)associated with the various sections (‘1’, . . . ‘12’) are plotted alongthe X axis. Stations 16 that are closer to the measurement system 30have a shorter cooling time and thus also have a higher radiation levelat the point in time when they pass by the measurement system 30. Thus,it can be seen in FIG. 7 that a glass product 18 from station ‘12B’,which is close to the measurement system 30 (see also FIG. 2), is hotterthan a glass product 18 from station ‘1B’, which is far away from themeasurement system 30. The graph obtained is termed the IS machine plot.

In FIG. 8 an exponential curve that has been calculated with the aid ofthe “least squares” or a similar method has been drawn through themeasurement points from FIG. 7. This curve is termed the cooling curve.If all glass products formed have the same glass wall thickness,temperature distribution and material characteristics after their finalshaping process, the measurement points of the IS machine plot will thenlie precisely on the cooling curve. The glass products 18 will all be ofthe same quality. If, however, a disturbance occurs in a process stepfor a specific section 14 (and thus station), the products originatingfrom this section 14 will be affected by a change in quality. Thetemperature distribution and/or the glass wall thickness will change. Asa result the IS machine plot will display a deviation with respect tothe cooling curve. If the measured intensities are on the cooling curve,the glass products 18 will then be of the same quality. The conclusionis then also that the cooling curve can be used as a reference value forthe shaping process. The values of IS machine setting parametersassociated with a specific cooling curve for a glass product 18 canserve as reference values for the future production of the glass product18.

When another type of glass product has to be produced, all settingparameters for the shaping process will then have to be adjusted. Toappreciably shorten this adjustment time and to reduce the large amountof guesswork, the (already known) setting parameters from the coolingcurve for the glass product are immediately used as reference value. Thesettings for the shaping process are now so adjusted that the IS machineplot becomes identical to the cooling curve. In this way all glassproducts 18 acquire the same quality as in the previous production.

By recording any deviations between a current IS machine plot and thecooling curve it is possible to indicate an error in the shaping processand to determine in which process step this error has occurred.Preferably, the IS machine plots and the cooling curves are determinedfor all set measurement regions 40, 41, 42, 43, 44 for the currentprocess. The calculated cooling curves are used as reference values foreach station. If a deviation occurs in the IS machine plot with respectto the cooling curve then the following situations can have arisen:

Situation A: The deviation applies to all sections and the newcalculated cooling curves have been shifted up or down compared with theexisting cooling curves, but the shape of the cooling curve has remainedvirtually the same.

Analysis A: A deviation has occurred for all sections. This means that afault has occurred in the entire IS machine, such as, for example, thecooling capacity for all sections, or a fault has occurred in theprocess steps upstream of the IS machine in the feeder, forehearth andmelting furnace. Furthermore, the fault is solely of a thermal nature.

Explanation: A station in a section can produce glass products 18independently of other sections. If a deviating radiation pattern withrespect to the cooling curve (the reference) is determined, the faultmust then have been caused by a common factor. This is either a commonfactor in the IS machine 6 (such as the temperature, humidity of thecooling air in the IS machine 6) or a common factor in the process stepsupstream of the IS machine 6. That is to say the temperature, materialcharacteristics in the feeder, forehearth and melting furnace 1. Theshape of the cooling curves has remained virtually the same. This meansthat the cooling rate of the products has also remained the same. It canthus be concluded that the initial temperature after the finalproduction step in the IS machine 6 has increased or decreased for allsections 14 and that both the glass distribution and the materialcharacteristics have remained the same.

Situation B: The deviation applies to all sections and the newcalculated cooling curves have shifted up or down compared with theexisting cooling curves but the shape of the cooling curve has alsochanged.

Analysis B: Once again there is a fault in all sections. Thus, the faultthat has occurred must be a common factor. Because the shape of thecooling curves has changed, it can be concluded that the materialcharacteristics of the glass have changed and that consequently theglass distribution has also changed.

Explanation: The shape of the cooling curves is dependent on the glassthickness of the glass wall and on the material characteristics but noton the initial temperature in the glass wall of the product. Since thequantity of glass remains virtually constant (gob), the deviation thathas occurred simultaneously for all sections 14 must have been caused bya change in the material characteristics.

Situation C: A deviation occurs only for the stations 16 that have acommon gob forming process.

Analysis C: If a deviation occurs in the IS machine plot compared withthe cooling curve only for the stations 16 that have a common gobforming process, the disturbance is then caused in the gob formingprocess. If the average intensity of the stations with a deviation ishigher or lower, the weight of the gob is then higher or lower.

Situation D: The deviation in the IS machine plot with respect to thecooling curve relates only to a single station 16.

Analysis D: A fault has occurred only in the station 16 concerned. Onlythose process components in the station can be the cause of the fault.

The embodiments described above are intended solely to serve as exampleand in no way are intended to limit the scope of the invention. A personskilled in the art will rapidly be able to devise other embodiments,such as, for example, the measurement of only a single bottle as afunction of time so that a cooling curve can be obtained by this means.The IS machine 6 can also be made up of a different composition ofsections 14 and stations 16, as a result of which the analytical methodsproceed somewhat differently. It will also be clear to a person skilledin the art that the digital processor 38 can be replaced by any othersuitable processor. The processor 38 can be constructed using analogue,digital or software techniques or any desired combination thereof. Theprocessor 38 can also consist of various sub-processes, optionally in amaster-slave relationship. The processor does not necessarily have to beclose to the rest of the system but can, for example, communicate withthe measurement system via remote communication.

1. Analytical system for analysing and controlling a production processfor glass products, the production process comprising a shaping processand a cooling process and the analytical system comprising aninfrared-sensitive measurement system and a processor communicatingtherewith, the infrared-sensitive measurement system being equipped tomeasure infrared radiation originating from hot glass productsimmediately after the shaping process for the glass products and theprocessor being equipped to determine a heat distribution in the glassproducts on the basis of information determined by the measurementsystem, characterised in that the infrared-sensitive measurement system(30) is sensitive only to radiation in the Near Infra Red (NIR) region.2. Analytical system according to claim 1, characterised in that theinfrared-sensitive measurement system (30) is sensitive to wavelengthsof between 900 and 2800 nanometers.
 3. Analytical system according toone of the preceding claims, characterised in that theinfrared-sensitive measurement system (30) comprises at least oneinfrared sensor (32) and at least one Near Infra Red filter (34). 4.Analytical system according to claim 3, characterised in that thetransmission characteristic of the Near Infra Red filter (34) isdependent on the colour and the specific material composition of theglass products.
 5. Analytical system according to one of the precedingclaims, characterised in that the processor (38) is equipped to carryout the following step: (a) subdividing an image of the glass products(18) into at least two measurement regions (40, 41, 42, 43, 44). 6.Analytical system according to claim 5, characterised in that theprocessor (38) is equipped to carry out the following step: (b)determining average intensity values for the different measurementregions for consecutive glass products (18).
 7. Analytical systemaccording to claim 6, characterised in that the processor (38) isequipped to carry out the following steps: (c) determining, for at leasttwo measurement regions, a current average value from the averageintensity values determined for a number of consecutively shaped glassproducts (18) over time; (d) recording, for each of the at least twomeasurement regions, any deviation between the current intensity or thecurrent average intensity and a reference value; (e) comparing anydeviations between the at least two measurement regions; (f) generatingan error signal in the event of any deviations.
 8. Analytical systemaccording to claim 7, characterised in that the error signal isindicative of a deviating glass thickness if a positive deviation occursin a first measurement region and a negative deviation occurs in asecond measurement region.
 9. Analytical system according to claim 7,characterised in that the error signal is indicative of a deviatingglass temperature if a positive deviation occurs for all measurementregions or a negative deviation occurs for all measurement regions. 10.Analytical system according to claim 6, characterised in that theprocessor (38) is equipped to carry out the following steps for at leastone measurement region: (c) determining a machine plot by plotting agraph of the average intensity values as a function of the consecutiveglass products (18), i.e. stations (14); (d) determining a cooling plotby means of an optimum fit curve; (e) recording any deviations between acurrent machine plot and the cooling plot; (f) generating an errorsignal in the event of any deviations.
 11. Analytical system accordingto claim 10, characterised in that the error signal contains informationon a possible cause during the shaping process.
 12. Analytical systemaccording to claims 1-3, characterised in that the processor (38) isequipped to record local discontinuities in the heat distribution in aglass product.
 13. Method for analysing and controlling a productionprocess for glass products, comprising: a) providing measurement meansfor determining a heat distribution in hot glass products; b) measuringinfrared radiation originating from the hot glass products before theseenter a cooling oven; c) determining a heat distribution in glassproducts on the basis of the infrared radiation measured, characterisedin that the measurement means (30) are sensitive only to radiation fromthe Near Infra Red region.
 14. Method according to claim 13,characterised in that the measurement means (30) are sensitive only towavelengths between 900 and 2800 nanometres.
 15. Method according toclaim 13, characterised in that the measurement means (30) comprise atleast one infrared sensor (32) and at least one Near Infra Red filter(34).
 16. Method according to one of claims 13-15, characterised in thatthe method comprises the following step: (d) subdividing an image of theglass products (18) into at least two measurement regions (40, 41, 42,43, 44).
 17. Method according to one of claims 13-16, characterised inthat the method comprises the following step: (e) determining averageintensity values for the different measurement regions for consecutiveglass products (18).
 18. Method according to one of claims 13-17,characterised in that the method comprises the following steps: (f)determining, for at least two measurement regions, a current averagevalue from the average intensity values determined for a number ofconsecutively shaped glass products (18); (g) recording, for each of theat least two measurement regions, any deviation between the currentaverage intensity and a reference value; (h) comparing any deviationsbetween the at least two measurement regions; (i) generating an errorsignal in the event of any deviations.
 19. Method according to claim 18,characterised in that the error signal is indicative of a deviatingglass thickness if a positive deviation occurs in a first measurementregion and a negative deviation occurs in a second measurement region.20. Method according to claim 18, characterised in that the error signalis indicative of a deviating glass temperature if a positive deviationoccurs for all measurement regions or a negative deviation occurs forall measurement regions.
 21. Method according to claim 17, characterisedin that the method comprises the following steps: (j) determining amachine plot by plotting a graph of the average intensity values as afunction of the consecutive glass products (18), i.e. stations (14); (k)determining a cooling plot by means of an optimum fit curve; (l)recording any deviations between a current machine plot and the coolingplot; (m) generating an error signal in the event of any deviations. 22.Method according to one of claims 13-15, characterised in that themethod comprises recording local discontinuities in the heatdistribution in the glass product.